This invention relates to piling.
1. Description of the Related Art
Present commercial pile driving practice utilizes piles having a variety of materials and geometric shapes to produce capacities in excess of 30 tons (about 270 kN). These piles are often concrete-filled steel tubes having closed-ends that are driven into a variety of soil types, including those with granular (sand and/or gravel) and cohesive (silt and/or clay) characteristics.
Generally, the piles have a constant cylindrical cross-section. However, it is well known that a gradually increasing tapered configuration often enhances the load bearing capacity of piles, particularly in granular soils. Thus, piles having such geometries, such as full-length fluted piles with tapered fluted bottom sections below a length of fluted cylindrical tubing having a diameter equal to that at the top of the tapered section, have been shown to be effective by producing higher capacities than cylindrical piles at similar penetrations into these soils. These piles have been used successfully for decades. They are described at pages 158 and 159 of the book xe2x80x9cFoundation Constructionxe2x80x9d by A. Brinton Corson published 1965 by McGraw-Hill Book Company.
2. Brief Summary of the Invention
The piles for this invention have tapered bottom sections made of steel tubing shaped into a polygon cross-section having substantially equal sides (preferably about 8-16, e.g. 12 sides), or of said polygonal cross-section having a short transitional length to a circular cross-section at the top, which is joined by a fabricated splicer, or by butt welding, to conventional circular steel cylindrical pipe having a diameter that may be equal to, or less than, the top diameter of the taper. Wall thicknesses for both the tapered section and pipe section can be up to 0.5 in. (about 13 mm) compared to 0.24 in. (about 6 mm) for the conventional fluted piles, top diameters of the tapered section may be from 12 in. (300 mm) to 24 in. (600 mm), bottom diameters may be from 8 in. (200 mm) to 20 in. (500 mm); tapered lengths may be fabricated in lengths of 5 to 40 feet (1.5 m to 12 m), and circular pipe lengths fabricated to lengths of 80 feet (24 m) and longer. For conventional fluted piles, the splice between the tapered section and cylindrical fluted section is a lap weld from the top of the tapered section to the side of the cylindrical section which has been inserted for several inches into the tapered section, maximum metal thickness is 0.24 in. (about 6 mm), tapered sections have a maximum upper diameter of 18 in. (about 450 mm) and bottom diameters are all 8 in. (about 200 mm), and cylindrical fluted sections are made to a maximum length of 40 ft. (about 12 m)
These piles will produce comparable and greater capacities than the previously described fluted piles.
Among the advantages of these piles are
1. A wide range of geometries and lengths for the tapered bottoms can be fabricated by means of existing equipment and technology, such as brake-forming. The pile length, top and bottom diameter, and wall thickness can be made to satisfy site-specific pile capacities and soil conditions.
2. Significant cost savings are possible by the use of conventional cylindrical pipe for the tops of these piles. Pipe costs considerably less than fluted cylindrical tubing. Added savings will result if the pipe diameter used is less than the top diameter of the tapered section, and by the re-use of pipe remaining from previously driven piles that can be easily spliced. Furthermore, the use in the practice of this invention of thin-walled pipe (or, alternatively, corrugated steel shell) that is driven with an internal mandrel will also produce significant cost-savings.
3. Specific design considerations not possible with existing configurations of piles having tapered bottoms may be designed for using the proposed piles. These include tapered and pipe wall thicknesses of up to 0.5 in. (about 13 mm) to provide stiffness and suitable stress levels for both driving conditions and service conditions. Heavier wall thicknesses may be used for the proposed piles to avoid damage often caused to fluted tapered piles with available maximum wall thickness. Added pile stiffness and strength also improves the driving efficiency thereby yielding improved pile load carrying capacity.
4. The splices for these piles may be drive-fit, weld-fit, or butt-welded. In all cases, the load transfer from the top of the pile to the bottom is made by continuous bearing of each of the components, and not through a shear transfer in a lap-welded splice as is customary for fluted piles. The convenience, effectiveness, and economy of these splices will make it possible to perform more splicing at the job site, thereby allowing the preferable and less costly shipment of shorter lengths.
5. The circular cylindrical pipe sections of these piles may be manufactured in lengths to 80 feet (about 25 m). Thus, the splicing of the pipe to a typical tapered section of 25 feet (about 8 m) will produce an overall length of up to 105 feet (about 33 m). Additional sections of pipe may be conveniently added, if needed, by the use of butt-welded splices or mechanical sleeves. Fluted piles generally have a fabrication length limitation for the cylindrical sections of 40 feet (about 12 m) which, with tapered lengths of 25 feet (about 8 m), will produce overall lengths of up to only 65 feet (about 20 m). Additional piling length requires costly splicing of the fluted cross-section. Thus, the use of the piles of this invention piles will often eliminate costly added splices when the total pile lengths are longer than 65 feet, and allow for effective and efficient splicing if needed at any length.